chore(plugins): remove stale SKILL.md stubs from plugin skill dirs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/git/skills/git-branch/SKILL.md

@@ -1,10 +0,0 @@
----
-name: git-branch
-description: >
-  Use when you want to create, switch, rename, or delete git branches.
-  Stub — full content not yet written.
-metadata:
-  category: implement
----
-
-> **Stub.** This skill is a placeholder. Content will be authored in a future workstream.

plugins/git/skills/git-commit/SKILL.md

@@ -1,10 +0,0 @@
----
-name: git-commit
-description: >
-  Use when you want to commit staged changes following conventional commit
-  format (feat:, fix:, docs:, chore:, etc.). Stub — full content not yet written.
-metadata:
-  category: implement
----
-
-> **Stub.** This skill is a placeholder. Content will be authored in a future workstream.

plugins/git/skills/git-flow/SKILL.md

@@ -1,10 +0,0 @@
----
-name: git-flow
-description: >
-  Use when you want to follow a complete git feature-branch workflow from
-  branch creation through merge. Stub — full content not yet written.
-metadata:
-  category: implement
----
-
-> **Stub.** This skill is a placeholder. Content will be authored in a future workstream.

plugins/git/skills/git-pr/SKILL.md

@@ -1,10 +0,0 @@
----
-name: git-pr
-description: >
-  Use when you want to open, review, or merge a pull request via the git
-  host CLI. Stub — full content not yet written.
-metadata:
-  category: implement
----
-
-> **Stub.** This skill is a placeholder. Content will be authored in a future workstream.